/**
 * 输入两个单调递增的链表，输出两个链表合成后的链表，当然我们需要合成后的链表满足单调不减规则。
 */
public class Solution25 {
    public ListNode Merge(ListNode list1, ListNode list2) {
        if (list1 == null && list2 == null) {
            return null;
        }

        if (list1 == null) {
            return list2;
        }

        if (list2 == null) {
            return list1;
        }

        ListNode result = null;
        ListNode resultCurrent = null;

        while (list1 != null && list2 != null) {
            if (list1.val <= list2.val) {
                if (result == null) {
                    result = list1;
                    resultCurrent = result;
                } else {
                    resultCurrent.next = list1;
                    resultCurrent = resultCurrent.next;
                }
                list1 = list1.next;
            } else {
                if (result == null) {
                    result = list2;
                    resultCurrent = result;
                } else {
                    resultCurrent.next = list2;
                    resultCurrent = resultCurrent.next;
                }
                list2 = list2.next;
            }
        }

        if (list1 == null) {
            resultCurrent.next = list2;
        } else {
            resultCurrent.next = list1;
        }

        return result;
    }
}
